PURIFICATION OF SECONDARY (2, 3) ALKYL SULFATE SURFACTANTS

Abstract: Secondary (2, 3) alkyl sulfate surfactants contaminated with inorganic sulfates such as sodium sulfate are washed with water at temperatures at or below the Krafft temperatures of said surfactants. The resulting, purified secondary alkyl sulfate surfactants are especially useful in the manufacture of homogeneous liquid or gel detergent compositions.

Description: PURIFICATION OF SECONDARY (2,3) ALKYL SULFATE SURFACTANTS FIELD OF THE INVENTION The present invention relates to a method for purifying secondary (2,3) alkyl sulfate surfactants, especially to remove unwanted inorganic sulfate contaminants. The resulting purified secondary (2,3) alkyl sulfates are preferred for use in the formulation of homogeneous liquid and stable gel detergents. BACKGROUND OF THE INVENTION Most conventional detergent compositions contain mixtures of various detersive surfactants in order to remove a wide variety of soils and stains from surfaces. For example, anionic surfactants, especially the alkyl benzene sulfonates, are useful for removing particulate soils, and nonionic surfactants, such as the alkyl ethoxylates and alkylphenol ethoxylates are useful for removing greasy soils. It has now been discovered that a particular sub-set of the class of secondary alkyl sulfates, referred to herein as secondary (2,3) alkyl sulfates, offers considerable advantages to the for ulator and user of detergent compositions. For example, the secondary alkyl (2,3) sulfates are more soluble in aqueous media than their counterpart primary alkyl sulfates of comparable chain lengths. Accordingly, they can be formulated as stable, homogeneous liquid detergents. The improved solubility of the secondary (2,3) alkyl sulfates also allows them to be formulated in the concentrated form now coming into vogue with both granular and liquid laundry detergents. In addition, it has now been determined that the secondary (2,3) alkyl sulfates are both aerobically and anaerobically degradable, which assists in their disposal in the environment. Of course, the manufacturer of fully-formulated detergent compositions is concerned not only with the safety, ease-of- handling and performance of the individual components of such compositions, but also with their ability to be formulated as stable compositions which are convenient and aesthetically pleasing to the user. One problem associated with the formulation of homogeneous liquid detergents is their tendency to separate into two or more phases on storage. Likewise, gel detergents have a strong tendency to "break" on storage, with partial or total liquefaction of the gel structure. Such problems become acute with the modern concentrated laundry detergents, especially those which contain multiple ionic ingredients which tend to promote phase separation and gel breakage. Another problem associated with ionic contaminants, particu¬ larly multivalent anions such as sulfate, is their tendency to precipitate from liquid formulations. Such problems are magnified if the formulations contain performance-enhancing amounts of divalent cations such as magnesium or calcium. In this regard, the conventional secondary (2,3) alkyl sulfates can present difficulties. The manufacturing process used with the secondary (2,3) alkyl sulfates typically involves the reaction of sulfuric acid with an olefin, followed by neutraliza¬ tion with base. During the neutralization step, excess sulfuric acid is converted into inorganic sulfate salts, such as sodium sulfate. The sulfate salts, being water-soluble, tend to remain with the neutralized secondary (2,3) alkyl sulfate surfactant which, of course, is also water-soluble. Since both the surfact¬ ant and the inorganic sulfate are water-soluble, they cannot be simply separated by an aqueous wash, since this would result in unacceptable losses of the surfactant. As a result, in commercial practice the secondary (2,3) alkyl sulfate surfactants are typic¬ ally contaminated with as much as 10% sodium sulfate. It has now been determined that the presence of the soluble sulfate contaminants in commercially available secondary (2,3) alkyl sulfate surfactants tends to add to the problem of phase separation and gel breakage in homogeneous liquid and gel deter¬ gent compositions. This potentially limits the usefulness of this otherwise desirable class of surfactants. By the present invention it has been discovered that second¬ ary (2,3) alkyl sulfate surfactants can be washed with water to decrease or remove the inorganic sulfate contaminants, but without unacceptable losses of the surfactant, itself. This desirable result is achieved by conducting the washing operation at or below the Krafft temperature of the surfactant. Substantially inorganic sulfate-free secondary (2,3) alkyl sulfate surfactants are thereby secured for use in homogeneous liquid and gel detergents, and for other uses where sulfate contamination may be undesirable. BACKGROUND ART Detergent compositions with various "secondary" and branched alkyl sulfates are disclosed in various patents; see: U.S. 2,900,346, Fowkes et al, August 18, 1959; U.S. 3,468,805, Grifo et al, September 23, 1969; U.S. 3,480,556, DeWitt et al , November 25, 1969; U.S. 3,681,424, Bloch et al, August 1, 1972; U.S. 4,052,342, Fernley et al, October 4, 1977; U.S. 4,079,020, Mills et al , March 14, 1978; U.S. 4,235,752, Rossall et al, November 25, 1980; U.S. 4,529,541, Wilms et al, July 16, 1985; U.S. 4,614,612, Reilly et al, September 30, 1986; U.S. 4,880,569, Leng et al, November 14, 1989; U.S. 5,075,041, Lutz, December 24, 1991; U.K. 818,367, Bataafsche Petroleum, August 12, 1959; U.K. 1,585,030, Shell, February 18, 1981; GB 2,179,054A, Leng et al, February 25, 1987 (referring to GB 2,155,031). U.S. Patent 3,234,258, Morris, February 8, 1966, relates to the sulfation of alpha olefins using H2SO4, an olefin reactant and a low boiling, nonionic, organic crystallization medium. SUMMARY OF THE INVENTION The present invention relates to the use of secondary (2,3) alkyl sulfate surfactants which are substantially free from water-soluble inorganic sulfate contaminants to prepare homogeneous liquid or gel detergent compositions which comprise said secondary (2,3) alkyl sulfate as a detersive surfactant, one or more conventional detersive adjuncts and a water-based carrier material. The invention provides a method for removing water-soluble inorganic sulfate contaminants from secondary (2,3) alkyl sulfate surfactants, comprising intimately contacting a substantially solid or pasty mixture of said surfactant and said contaminants with wash water, said contact being at a temperature that is no greater than the Krafft temperature, and is preferably below the Krafft temperature, of said surfactant, for a time sufficient to dissolve all or part of said inorganic sulfate contaminants, and removing said wash water containing said dissolved sulfate contaminants from contact with said surfactant. In a preferred mode, the aqueous washing process is conducted for a time sufficient to remove at least 50%, preferably at least 90%, of said inorganic contaminants. The method herein is especially useful when the surfactant is a C10-C20 secondary (2,3) alkyl sulfate, and mixtures thereof. In such circumstances, it is preferred that the contact between the water and the contaminated secondary (2,3) alkyl sulfate surfact- ant be carried out at a temperature no higher than about 22 * C, preferably no higher than about 20 * C for Ciβ-Ciβ compounds and no higher than about lO'C for C14 compounds. An additional advantage of the invention is that it addition¬ ally reduces the levels of any secondary (4) alkyl sulfate, secondary (5) alkyl sulfate, secondary (6) alkyl sulfate, and the like, surfactant contaminants which may be co-present with said secondary (2,3) alkyl sulfate surfactant. All percentages, ratios and proportions herein are by weight, unless otherwise specified. All documents cited are incorporated herein by reference. DETAILED DESCRIPTION OF THE INVENTION Secondary (2,3) Alkyl Sμlfa e Sμrfa taηt? For the convenience of the formulator, the following identi¬ fies and illustrates the differences between the sulfated surfact- ants employed herein and otherwise conventional alkyl sulfate surfactants. Conventional primary alkyl sulfate surfactants have the general formula ROSO3-M+ wherein R is typically a linear C10-C20 hydrocarbyl group and M is a water-solubilizing cation. Branched-chain primary alkyl sulfate surfactants (i.e., branched-chain "PAS") having 10-20 carbon atoms are also known; see, for example, European Patent Application 439,316, Smith et al , filed 21.01.91. Conventional secondary alkyl sulfate surfactants are those materials which have the sulfate moiety distributed randomly along the hydrocarbyl "backbone" of the molecule. Such materials may be depicted by the structure CH 3 (CH2)n(CHOSθ3-M+)(CH 2 )n-CH3 wherein m and n are integers of 2 or greater and the sum of m + n is typically about 9 to 17, and M is a water-solubilizing cation. By contrast with the above, the selected secondary (2,3) alkyl sulfate surfactants used herein comprise structures of formulas A and B (A) CH3(CH2)χ(CHOSθ3-M+) CH3 and (B) CH3(CH2)y(CH0S03-M+) CH2CH3 for the 2-sulfate and 3-sulfate, respectively. Mixtures of the 2- and 3-sulfate can be used herein. In formulas A and B, x and (y+1) are, respectively, integers of at least about 6, and can range from about 7 to about 20, preferably about 10 to about 16. M is a cation, such as an alkali metal, ammonium, alkanolammonium, alkaline earth metal, or the like. Sodium is typical for use as M to prepare the water-soluble (2,3) alkyl sulfates, but ethanolam¬ monium, diethanolammonium, triethanolammonium, potassium, ammon¬ ium, and the like, can also be used. It will be appreciated that changes in the cations will change the preferred temperatures for washing the secondary (2,3) alkyl sulfates, due to changes in the Krafft temperature. By the present invention it has been determined that the physical/chemical properties of the foregoing types of alkyl sulfate surfactants are unexpectedly different, one from another, in several aspects which are important to for ulators of various types of detergent compositions. For example, the primary alkyl sulfates can disadvantageously interact with, and even be precipi¬ tated by, metal cations such as calcium and magnesium. Thus, water hardness can negatively affect the primary alkyl sulfates to a greater extent than the secondary (2,3) alkyl sulfates herein. Accordingly, the secondary (2,3) alkyl sulfates have now been found to be preferred for use in the presence of calcium ions and under conditions of high water hardness, or in the so-called "under-built" situation which can occur when low levels of builders or nonphosphate builders are employed. Importantly, when formulating concentrated liquid detergents with calcium or magnesium ions to enhance grease cutting or sudsing performance, or to provide enzyme stability, it has now been found that the primary alkyl sulfates can be problematic due to such interactions with calcium or magnesium cations. Moreover, the solubility of the primary alkyl sulfates is not as great as the secondary (2,3) alkyl sulfates. Hence, the formulation of high-active surfactant particles and high-concentrate liquid detergents has now been found to be simpler and more effective with the secondary (2,3) alkyl sulfates than with the primary alkyl sulfates. With regard to the random secondary alkyl sulfates (i.e., secondary alkyl sulfates with the sulfate group at positions such as the 4, 5, 6, 7, etc. secondary carbon atoms), such materials tend to be tacky solids or, more generally, pastes. Thus, the random alkyl sulfates do not afford the processing advantages associated with the solid secondary (2,3) alkyl sulfates when formulating detergent granules, bars, or tablets. Moreover, the secondary (2,3) alkyl sulfates herein provide better sudsing than the corresponding random mixtures. It is preferred that the secondary (2,3) alkyl sulfates be substantially free (i.e., contain less than about 20%, more preferably less than about 10%, most preferably less than about 5%) of such random secondary alkyl sulfates. One additional advantage of the secondary (2,3) alkyl sulfate surfactants herein over other positional or "random" alkyl sulfate isomers is in regard to the improved benefits afforded by said secondary (2,3) alkyl sulfates with respect to soil redeposition in the context of fabric laundering operations. As is well-known to users, laundry detergents loosen soils from fabrics being washed and suspend the soils in the aqueous laundry liquor. However, as is well-known to detergent formulators, some portion of the suspended soil can be redeposited back onto the fabrics. Thus, some redistribution and redeposition of the soil onto all fabrics in the load being washed can occur. This, of course, is undesirable and can lead to the phenomenon known as fabric "greying". (As a simple test of the redeposition characteristics of any given laundry detergent formulation, unsoiled white "tracer" cloths can be included with the soiled fabrics being laundered. At the end of the laundering operation the extent that the white tracers deviate from their initial degree of whiteness can be measured photometrically or estimated visually by skilled observers. The more the tracers' whiteness is retained, the less soil redeposition has occurred.) It has now been determined that the secondary (2,3) alkyl sulfates afford substantial advantages in soil redeposition characteristics over the other positional isomers of secondary alkyl sulfates in laundry detergents, as measured by the cloth 5 tracer method noted above. Thus, the selection of secondary (2,3) alkyl sulfate surfactants according to the practice of this invention which preferably are substantially free of other positional secondary isomers unexpectedly assists in solving the problem of soil redeposition in a manner not heretofore 10 recognized. It is to be noted that the secondary (2,3) alkyl sulfates used herein are quite different in several important properties from the secondary olefin sulfonates (e.g., U.S. Patent 4,064,076, Klisch et al, 12/20/77); accordingly, the secondary sulfonates are 15 not the focus of the present invention. The preparation of the secondary (2,3) alkyl sulfates of the type useful herein can be carried out by the addition of H2SO4 to olefins. A typical synthesis using α-olefins and sulfuric acid is 2 disclosed in U.S. Patent 3,234,258, Morris, or in U.S. Patent 5,075,041, Lutz, granted December 24, 1991. The synthesis, conducted in solvents which afford the secondary (2,3) alkyl sulfates on cooling, yields products which, when purified to remove the unreacted materials, randomly sulfated materials, unsulfated by-products such as C\o and higher alcohols, secondar olefin sulfonates, and the like, are typically 90+% pure mixtures of 2- and 3-sulfated materials (up to 10% sodium sulfate is - • - • - ■ typically present) and are white, non-tacky, apparently crystalline, solids. Some 2,3-disulfates may also be present, but generally comprise no more than 5% of the mixture of secondary (2,3) alkyl mono-sulfates. Such materials are available as under the name "DAN", e.g., "DAN 200" from Shell Oil Company. 0 When formulating liquid compositions, especially clear liquids, it has now been found to be preferred that the secondary (2,3) alkyl sulfate surfactants contain less than about 3% sodium sulfate, preferably less than about 1% sodium sulfate. In and of itself, sodium sulfate is an innocuous material. However, it * - * dissolves and adds to the ionic "load" in aqueous media, and this can contribute to phase separation in the liquid compositions, or to crystal formation, or to gel breaking in the gel compositions. Sulfate removal is accomplished by the present invention, as disclosed hereinafter. Aqueous Washing Process Various means can be used to lower the sodium sulfate content of the secondary (2,3) alkyl sulfates. For example, when the H2SO4 addition to the olefin is completed, care can be taken to remove unreacted H2SO4 before the acid form of the secondary (2,3) alkyl sulfate is neutralized. In the present method, the sodium salt form of the secondary (2,3) alkyl sulfate which contains sodium sulfate can be rinsed with water at a temperature near the Krafft temperature of the sodium secondary (2,3) alkyl sulfate. This will remove Na2Sθ4 with only minimal loss of the desired, purified sodium secondary (2,3) alkyl sulfate. Of course, both procedures can be used, the first as a pre-neutralization step and the second as a post-neutralization step. The term "Krafft temperature" as used herein is a term of art which is well-known to workers in the field of surfactant sciences. Krafft temperature is described by K. Shinoda in the text "Principles of Solution and Solubility", translation in collaboration with Paul Becher, published by Marcel Dekker, Inc. 1978 at pages 160-161. Stated succinctly, the solubility of a surface active agent in water increases rather slowly with temperature up to that point, i.e., the Krafft temperature, at which the solubility evidences an extremely rapid rise. At a temperature approximately 4'C above the Krafft temperature a solution of almost any composition becomes a homogeneous phase. In general, the Krafft temperature of any given type of surfactant, such as the secondary (2,3) alkyl sulfates herein which comprise an anionic hydrophilic sulfate group and a hydrophobic hydrocarbyl group, will vary with the chain length of the hydrocarbyl group. This is due to the change in water solubility with the variation in the hydrophobic portion of the surfactant molecule. In the practice of the present invention the formulator will wash the secondary (2,3) alkyl sulfate surfactant which is contaminated with sodium sulfate with water at a temperature that is no higher than the Krafft temperature, and which is preferably lower than the Krafft temperature, for the particular secondary (2,3) alkyl sulfate being washed. This allows the sodium sulfate to be dissolved and removed with the wash water, while keeping losses of the secondary (2,3) alkyl sulfate into the wash water to a minimum. Under circumstances where the secondary (2,3) alkyl sulfate surfactant herein comprises a mixture of alkyl chain lengths, it will be appreciated that the Krafft temperature will not be a single point but, rather, will be denoted as a "Krafft boundary". Such matters are well-known to those skilled in the science of surfactant/solution measurements. In any event, for such mixtures of secondary (2,3) alkyl sulfates, it is preferred to conduct the sodium sulfate removal operation at a temperature which is below the Krafft boundary, and preferably below the Krafft temperature of the shortest chain-length surfactant present in such mixtures, since this avoids excessive losses of secondary (2,3) alkyl sulfate to the wash solution. For example, for Cχ6 secondary sodium alkyl (2,3) sulfate surfactants it is preferred to conduct the washing operation at temperatures below about 30 * C, preferably below about 20 * C. The washing process can be conducted batchwise by suspending wet or dry secondary (2,3) alkyl sulfates in sufficient water to provide 10-50% solids, typically for a mixing time of at least 10 minutes at about 22 * C (for a Ciβ secondary [2,3] alkyl sulfate), followed by pressure filtration. In a preferred mode, the slurry will comprise somewhat less than 35% solids, inasmuch as such slurries are free-flowing and amenable to agitation during the washing process. As an additional benefit, the washing process also reduces the levels of organic contaminants which comprise the random secondary alkyl sulfates noted above. Adjunct Ingredients The purified secondary (2,3) alkyl sulfate surfactants herein, particularly in the sodium salt form, are typically used in combination with other, conventional adjunct detersive ingredients in fully-formulated detergent compositions which can be used for laundering, hard surface cleaning (including dish- care), personal hygiene, and the like. The compositions are preferably in the form of homogeneous liguids which comprise from about 5% to about 50% by weight of the purified secondary (2,3) alkyl sulfate surfactants. Preferred, stable, homogeneous gel compositions comprising from about 5% to about 50% by weight of the purified secondary (2,3) alkyl sulfate surfactants are also provided. If desired, the purified secondary (2,3) alkyl sulfates can also be employed to prepare detergent granules, powders, flakes, bars and the like. In preparing such compositions, it is typical for the formulator to add various surfactants, builders, detersive enzymes, brighteners, bleaches and bleach activators, soil release agents, and the like, which are designed to enhance the overall cleaning performance and/or aesthetic benefits of the compositions. Indeed, when adding such ingredients to liquid and gel compositions, especially at high concentrations, the problems associated with separation and/or gel breakage are most likely to occur due to the enhanced ionic "load" in such compositions. However, use of the purified secondary (2,3) alkyl sulfate surfactants afforded by the present invention assist the formulator in that the nondetersive sodium sulfate contaminants are not present to further add to the overall ionic load of such formulations. It will be appreciated by the formulator skilled in the detergency arts that all manner of such adjunct ingredients can be employed with the purified secondary (2,3) alkyl sulfates. However, the following listing is mentioned herein by way of exemplification, and not by limitation, of such ingredients. Enzymes such as proteases, amylases, cellulases, Upases, peroxidases, and the like, and mixtures thereof, can be employed in the present compositions at levels from about 0.001% to about 5%. Such detersive enzyme materials are available from many commercial sources. Enzyme stabilizers such as boric acid and the borates, substituted boric acids, and the like, can also be present in enzyme-containing compositions, typically at levels from 0.25% to about 10%. Water-soluble detergency builders at levels from about 5% to about 50% can be present in the liquid and gel compositions. Water-soluble builders such as the polycarboxylates, particularly the citrates, oxydisuccinates, tartrates, and the like, can be used in such compositions. If desired, bleaching agents such as the perborates, the persulfates, the percarbonates, and combinations thereof with well-known bleach activators such as tetraacetylethylenediamine ("TAED") and nonanoyloxybenzene sulfonate ("NOBS") can be used in such compositions, typically at levels from about 5% to about 20%. Conventional oligomeric soil release agents including cellulose-based materials and the nonionic and anionic ester materials well-known in the detergency arts can also be employed in the present compositions, typically at levels from about 0.1% to about 10%. Clay soil removal and antiredeposition agents such as the ethoxylated polyamino materials, carboxy ethyl cellulose, and the like can optionally be employed in the present compositions at levels from about 0.01% to about 10%. Chelating agents such as the amino phosphonates and the biodegradable chelant ethylenediaminedisuccinate (EDDS), can optionally be employed in the compositions herein. If used, chelating agents are typically present at levels from about 0.1% to about 3%. Polymeric dispersing agents such as the polymeric polycar¬ boxylates and polyethyleneglycols can be used in the present compositions at levels from about 0.1% to about 7%. Polyaspartate and polyglutamate dispersing agents are biodegradable and are especially preferred for such use. Any optical brighteners or other brightening or whitening agents known in the art can be incorporated in the present compositions at levels typically from about 0.05% to about 1.2%. Commercial optical brighteners include derivatives of stilbene, pyrazoline, cou arin, and the like, are well known in the trade literature. Through-the-wash fabric softeners can also be employed in the present compositions at levels from about 0.5% to about 10%. Such materials include clay softeners and various amine and cationic softeners such as those described in U.S. Patents 4,375,416 and 4,291,071. Adjunct Surfactants - The compositions herein can optionally contain various anionic, nonionic, zwitterionic, etc. surfactants. If used, such adjunct surfactants are typically present at levels of from about 1% to about 35% of the compositions. However, it is to be understood that the incorporation of adjunct anionic surfactants is entirely optional herein, inasmuch as the cleaning performance of the secondary (2,3) alkyl sulfates is excellent and these materials can be used to entirely replace surfactants such as the alkyl benzene sulfonates in fully-formulated detergent compositions. However, some adjunct surfactants, e.g., the betaines, sultaines and amine oxides are especially useful when high sudsing is desired, i.e., especially in hand dishwashing operations. Nonlimiting examples of optional surfactants useful herein include the conventional Cπ-Ciβ alkyl benzene sulfonates and primary and random alkyl sulfates, the Cio-Ciβ alkyl alkoxy sulfates (especially EO 1-5 ethoxy sulfates), the Cio-Ciβ alkyl alkoxy carboxylates (especially the EO 1-5 ethoxycarboxylates), the Cio-Ciβ alkyl polyglycosides and their corresponding sulfated polyglycosides, C12-C18 alpha-sulfonated fatty acid esters, C12-C18 alkyl and alkyl phenol alkoxylates (especially ethoxylates and mixed ethoxy/propoxy), Ci2 _c 18 betaines and sulfobetaines ("sultaines"), Cjo-Ciβ amine oxides, and the like. Other conven¬ tional useful surfactants are listed in standard texts. One particular class of adjunct nonionic surfactants especially useful herein comprises the polyhydroxy fatty acid amides of the formula: 0 Rl (I) R 2 - C - N - Z wherein: R 1 is H, Ci-Cβ hydrocarbyl, 2-hydroxyethyl, 2-hydroxy- propyl, or a mixture thereof, preferably C1-C4 alkyl, more prefer¬ ably Ci or C2 alkyl, most preferably Ci alkyl (i.e., methyl); and R 2 is a C5-C32 hydrocarbyl moiety, preferably straight chain C7-C19 alkyl or alkenyl, more preferably straight chain C9-C17 alkyl or alkenyl, most preferably straight chain C11-C19 alkyl or alkenyl, or mixture thereof; and Z is a polyhydroxyhydrocarbyl moiety having a linear, hydrocarbyl chain with at least 2 (in the case of glyceraldehyde) or at least 3 hydroxyls (in the case of other reducing sugars) directly connected to the chain, or an alkoxylated derivative (preferably ethoxylated or propoxylated) thereof. Z preferably will be derived from a reducing sugar in a reductive a ination reaction; more preferably Z is a glycityl moiety. Suitable reducing sugars include glucose, fructose, maltose, lactose, galactose, mannose, and xylose, as well as glyceraldehyde. As raw materials, high dextrose corn syrup, high fructose corn syrup, and high maltose corn syrup can be utilized as well as the individual sugars listed above. These corn syrups may yield a mix of sugar components for Z. It should be understood that it is by no means intended to exclude other suitable raw materials. Z preferably will be selected from the group consisting of -CH2-(CHOH) n -CH2θH, -CH(CH2θH)-(CHOH)„-l- CH2OH, -CH2-(CHOH)2(CHOR')(CHOH)-CH2θH, where n is an integer from 1 to 5, inclusive, and R' is H or a cyclic mono- or poly- saccharide, and alkoxylated derivatives thereof. Most preferred are glycityls wherein n is 4, particularly -CH2-(CHOH)4-CH2θH. In Formula (I), R can be, for example, N-methyl, N-ethyl, N-propyl, N-isopropyl, N-butyl, N-isobutyl, N-2-hydroxy ethyl, or N-2-hydroxy propyl. For highest sudsing, R is preferably methyl or hydroxyalkyl . If lower sudsing is desired, R* is preferably C2-C8 alkyl, especially n-propyl, iso-propyl, n-butyl, iso-butyl, pentyl, hexyl and 2-ethyl hexyl. R 2 -C0-N< can be, for example, cocamide, stearamide, oleamide, lauramide, myristamide, capricamide, palmitamide, tallowamide, etc. While polyhydroxy fatty acid amides can be made by the process of Schwartz, U.S. 2,703,798, contamination with cyclized by-products and other colored materials can be problematic. As an overall proposition, the preparative methods described in WO-9,206,154 and WO-9,206,984 will afford high quality polyhydroxy fatty acid amides. The methods comprise reacting N-alkylamino polyols with, preferably, fatty acid methyl esters in a solvent using an alkoxide catalyst at temperatures of about 85 * C to provide high yields (90-98%) of polyhydroxy fatty acid amides having desirable low levels (typically, less than about 1.0%) of sub-optimally degradable cyclized by-products and also with improved color and improved color stability, e.g., Gardner Colors below about 4, preferably between 0 and 2. (With compounds such as butyl, iso-butyl and n-hexyl, the methanol introduced via the catalyst or generated during the reaction provides sufficient fluidization that the use of additional reaction solvent may be optional.) If desired, any unreacted N-alkylamino polyol remaining in the product can be acylated with an acid anhydride, e.g., acetic anhydride, maleic anhydride, or the like, to minimize the overall level of such residual amines in the product. Resi¬ dual sources of classical fatty acids, which can suppress suds, can be depleted by reaction with, for example, triethanolamine. By "cyclized by-products" herein is meant the undesirable reaction by-products of the primary reaction wherein it appears that the multiple hydroxyl groups in the polyhydroxy fatty acid amides can form ring structures which are, in the main, not readily biodegradable. It will be appreciated by those skilled in the chemical arts that the preparation of the polyhydroxy fatty acid amides herein using the di- and higher saccharides such as maltose will result in the formation of polyhydroxy fatty acid amides wherein linear substituent Z (which contains multiple hydroxy substituents) is naturally "capped" by a polyhydroxy ring structure. Such materials are not cyclized by-products, as defined herein. The foregoing polyhydroxy fatty acid amides can also be sulfated, e.g., by reaction with Sθ3/pyridine, and the resulting sulfated material used as an adjunct anionic surfactant herein. Other Ingredients - A wide variety of other ingredients useful in detergent compositions can be included in the composi¬ tions herein, including other active ingredients, carriers, hydrotropes, processing aids, dyes or pigments, solvents for liquid formulations, etc. If high sudsing is desired, suds boosters such as the C10-C16 alkanolamides can be incorporated into the compositions, typically at 1%-10% levels. The C10-C14 monoethanol and diethanol amides illustrate a typical class of such suds boosters. Use of such suds boosters with high sudsing adjunct surfactants such as the amine oxides, betaines and sultaines noted above is also advantageous. Alternatively, if desired, suds controlling agents such as secondary Cio-Ciβ alcohols, hydrocarbons, fatty acids and silicones can be used in the compositions at levels of 0.1%-3%, by weight. Liquid detergent compositions can contain water and other solvents as carriers. Low molecular weight primary or secondary alcohols exemplified by methanol, ethanol, propanol, and isopropanol are suitable. Monohydric alcohols are preferred for solubilizing surfactant, but polyols such as those containing from 2 to about 6 carbon atoms and from 2 to about 6 hydrox groups (e.g., 1,3-propanediol, ethylene glycol, glycerine, and 1,2- propanediol) can also be used. The compositions may contain from 5% to 90%, typically 10% to 50% of such carriers. Gel compositions can comprise an aqueous carrier and can contain 0.5%-10%, or more, of various synthetic and natural gelling agents such as alginates and natural gums, as well as urea and urea derivatives. The detergent compositions herein will preferably be formulated such that during use in aqueous cleaning operations, the wash water will have a pH of between about 6.5 and about 11, preferably between about 7.5 and about 10.5 for fabric laundering. Liquid dishwashing product formulations preferably have a pH between about 6.8 and about 9.5. Techniques for controlling pH at recommended usage levels include the use of buffers, alkalis, acids, etc., and are well known to those skilled in the art. The C10-C20 secondary (2,3) alkyl sulfates can conveniently be employed herein. The C14-C18 compounds are preferred for laundry cleaning operations. The C12-C16 compounds are preferred for dishwashing compositions. The following are typical, nonlimiting examples which illustrate the detergent compositions and uses of the secondary ( » 3) alkyl sulfates purified according to this invention. For most purposes, the preferred compositions herein are free of phosphate builders. EXAMPLE I A liquid laundry detergent composition herein comprises the following. Ingredient % (wt.) Secondary (2,3) alkyl sulfate* 15.0 C14 N-methyl glucamide 5.0 Sodium citrate 3.0 C o alcohol ethoxylate (3) 13.0 Monoethanolamine 2.5 MAXATASE (enzyme) 0.5 LIPOLASE (enzyme) 0.5 Water/propylene glycol/ethanol (100:1:1) Balance *Ci4-Ci6 average chain length; Na salt form; less than 1% Na2S04. EXAMPLE II A liquid dishwashing composition with high grease removal properties is as follows. Ingredient % (wt.) Cχ2 N-methyl glucamide 9 .0 C12 ethoxy (1) sulfate 5 .0 Cu secondary (2,3) alkyl sulfate (Na)* 6, .5 C12 ethoxy (2) carboxylate 4, .5 C12 alcohol ethoxylate (4) 3, .0 C 2 amine oxide 3, .0 Sodium cumene sulfonate 2. .0 Ethanol 4. .0 Mg++ (as MgCl2) 0. .2 Ca ++ (as Ca formate) 0. .4 Water Balance ♦ Purified to contain less than 1% Na2S04. The following Example uses secondary (2,3) alkyl sulfates purified in the present manner to prepare gel dishwashing compositions. EXAMPLE III Gel compositions are as follows. To 0.8 grams of magnesium sulfate, 0.8 grams of Ca formate and 6.7 grams of cocoamido propyl betaine (30% active, Albright- Wilson, United Kingdom) dissolved in 25 grams of water, 8 grams of C91-8T Oobanol (100% active, Shell, USA), 1.00 grams of boric acid and 20 grams of urea (99% active, Fisher Scientific, USA) are added and mixed at 71-74'C. Once a homogeneous mixture is obtained, 8 grams of 97.6% active coconut N-methyl glucamide and 28 grams of sodium Cχ6 secondary (2,3) alkyl sulfate are added and agitation is continued. (Ingredients such as detersive enzymes can be added when the temperature of the liquid reaches about 35-40'C.) The final liquid product forms a gel on cooling. In an alternate mode, a gel is provided without urea. To a solution formed by dissolving 0.002 grams of blue dye in 42 grams of water at 62 * C, 0.25 grams of MgS04, 0.25 grams of CaCl2, 0.50 grams of perfume and 35% of 50% coconutalkyl C12-C14 N-methyl glucamide paste are added with agitation. Once all the materials are dissolved, 21 grams of an 80% sodium C12-14 secondary (2,3) alkyl sulfate paste is added. The solution is stirred for an additional 30 minutes at 77 * C. At about 40 * C, 0.5 grams of a commercial detersive protease composition is added and stirring is continued. Once stirring is stopped, the viscous liquid quickly solidifies into a gel after cooling. While the preferred compositions herein are in the form of stable, homogeneous liquids and gels, other forms such as bars, granules and the like are also provided herein.

Claims: What is claimed is: — 18 — 1. Use of secondary (2,3) alkyl sulfate surfactants which are substantially free from water-soluble inorganic sulfate contaminants to prepare homogeneous liquid or gel detergent compositions which comprise said secondary (2,3) alkyl sulfate as a detersive surfactant, one or more conventional detersive adjuncts and a water-based carrier material. 2. A process for removing water-soluble inorganic sulfate con¬ taminants from secondary (2,3) alkyl sulfate surfactants, comprising intimately contacting a substantially solid or pasty mixture of said surfactant and said contaminant with wash water, said contact being at a temperature that is no greater than the Krafft temperature of said surfactant, for a time sufficient to dissolve all or part of said inorganic sulfate contaminants, and removing said wash water containing said dissolved sulfate contaminants from contact with said surfactant. 3. A process according to Claim 2 which is conducted below the Krafft temperature of said surfactant. 4. A process according to either of Claims 2 or 3 wherein the surfactant is a C, Q -C, g secondary (2,3) alkyl sulfate, and mixtures thereof. 5. A process according to any of Claims 2-4 wherein the contact between the water and the contaminated secondary (2,3) alkyl sulfate surfact- ant is carried out at a temperature no higher than 20°C. 6. A process according to any of Claims 2-5 wherein the washing operation removes at least 50% by weight of the inorganic sulfate contaminants. 7. A process according to any of Claims 2-6 which additionally reduces the levels of any secondary (4) alkyl sulfate, secondary (5) alkyl sulfate, secondary (6) alkyl sulfate, and the like, surfactant contaminants from said secondary (2,3) alkyl sulfate surfactant.

Inventors: MURCH BRUCE PRENTISS, MURCH, BRUCE, PRENTISS
Applicants: PROCTER & GAMBLE, THE PROCTER & GAMBLE COMPANY
Application year: 1994
Main classification: C11D1
IPC codes: C07C303, C07C305, C11D1, C11D17